1. Technical Field
The present invention relates to a lens device, and more particularly, to a lens device including a lock mechanism that locks an operating ring, such as a focus ring or a zoom ring, at a desired position and is used for, for example, a monitoring camera.
2. Related Art
In recent years, small monitoring cameras (CCTV monitoring cameras) have come into widespread use in financial institutions and various kinds of stores. In the monitoring lens device used in this type of monitoring camera, a focus ring for adjusting a focus position and a zoom ring for adjusting a focal length are provided in an outer circumferential portion of a barrel (fixed cylinder). For example, when the monitoring camera is installed, an operator manually operates the focus ring and the zoom ring to adjust the focus position and the focal length.
In addition, the monitoring camera is provided on, for example, the wall while being accommodated in a case, and the front surface of a lens device for a monitoring camera faces the outside through an opening formed in the case to capture the outside. Patent Document 1 discloses a lens device for a monitoring camera in which a focus ring is provided on the front side (object side) of an outer circumferential portion of a barrel and a zoom ring is provided in an outer circumferential portion of the focus ring, which enables a user to easily operate the focus ring and the zoom ring through an opening formed in a case (see Patent Document 1 (JP-A-2007-310228 corresponding to US-A-2007/0268596)).
However, the lens device for a monitoring camera disclosed in Patent Document 1 is provided with a lock mechanism that fixes the focus ring and the zoom ring at the adjusted position. According to this structure, a screw hole is formed in the focus ring, and an opening portion is formed in the zoom ring at a position opposite to the screw hole so as to be elongated in a circumferential direction. A lock knob having a flange portion passes through the opening portion of the zoom ring and is engaged with the screw hole of the focus ring. When the lock knob is screwed after the focus ring and the zoom ring are operated to adjust focus and a focal length, the leading end of the lock knob passing through the screw hole of the focus ring comes into contact with the barrel, and the rotational position of the focus ring is fixed. In addition, the flange portion of the lock knob comes into contact with the periphery of the opening portion of the zoom ring, and the zoom ring is pressed against the flange portion and is fixed at the position.
When the focus ring and the zoom ring are locked by the lock mechanism, the flange portion of the lock knob comes lastly into contact with the zoom ring when the lock knob is fully tightened. In this case, when the flange portion comes into contact with the zoom ring with non-uniform pressure due to friction between the flange portion and the zoom ring, the rotating force of the lock knob is likely with the friction to act as the rotating force of the zoom ring. Therefore, when the lock knob is tightened, the zoom ring is displaced from the adjusted position or both the lock knob and the focus ring are displaced from the adjusted position. As a result, the focus position or the focal length deviates from the adjusted position before the rings are locked by the lock knob. In recent years, with an improvement in the image quality of monitoring cameras and an increase in the resolution thereof, focusing or the adjustment of an angle of view has been strictly performed. It is necessary to appropriately prevent deviations from the adjusted position.